Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$42.84	11.510%	$47.7709	$47.77	$47.75	$47.80
Purchase #2	$20.70	4.772%	$21.6878	$21.69	$21.70	$21.70
Purchase #3	$150.32	12.125%	$168.5463	$168.55	$168.55	$168.50
Purchase #4	$181.84	4.206%	$189.4882	$189.49	$189.50	$189.50
Purchase #5	$40.54	13.574%	$46.0429	$46.04	$46.05	$46.00
Purchase #6	$182.72	3.341%	$188.8247	$188.82	$188.80	$188.80
Purchase #7	$205.86	9.499%	$225.4146	$225.41	$225.40	$225.40
7 purchase totals =	$824.82		$887.7754	$887.77	$887.75	$887.70